Existing fire alarm and intrusion alarm systems suffer from a number of weaknesses which have resulted from the revolutionary growth of these types of systems. Such alarm installations typically consist of a variety of different types of sensors connected in a series loop, such as a McCullough loop, such that any sensor which alarms will trigger a local or remote station alarm. With such a system, there is no way of telling at the remote location which sensor has alarmed; and this results in problems both in locating the area where an actual intrusion has occurred and in trouble-shooting a system for recurring false alarms.
Very little standardization exists in this area. It frequently happens that within one installation, different types of wires, interconnection techniques, and sensors are used to provide similar protection. This wide diversity of installation practices complicates both the installation of such a system and later trouble-shooting or servicing, especially where such servicing is done by someone not familiar with the original installation.
Because of this lack of compatibility, there are generally no centralized test provisions. Individual sensors require different methods of testing, and in general, someone must actually go to each sensor to perform the test locally. Also, the security of such a system is generally poor. Sensors may easily be jumpered out, and short or open circuits can develop which eliminate sensors from the system without any indication thereof.